Among all the intriguing properties of water ice, porosity is surely one of the most unexpected to date. There are many different forms of ice, and the discovery of one of these in particular, ice XVII, opened the route to study these ice structures for their gas absorption and desorption properties. The simplicity and abundance of water make the concept of ice as a storage material extremely appealing.
Ice XVII has a low-density, is highly porous, and presents accessible spiralling channels where different types of gas can be reversibly hosted in an essentially one-dimensional geometry. A similar property has also been observed by adding helium to another form of ice, ice XVI, further enhancing the fundamental and applicative interest in these low-density materials.
In this study, published in Journal of Chemical Physics, researchers from the Consiglio Nazionale delle Ricerche and ISIS used ice XVII made with D2O as a porous matrix to host molecular hydrogen, nitrogen and oxygen at near ambient pressure (0.5-3 bar) and low temperature (20-90 K). By combining the high-resolution spectroscopic techniques of Raman scattering, performed in the CNR-IFAC laboratory (Florence, Italy), and Inelastic Neutron Scattering (INS) performed on the TOSCA spectrometer, the team were able to fully characterise the microscopic vibrational dynamics of these confined guest molecules in the channel-like environment within the ice.
They were able to clearly resolve both the rotational and rattling modes for the lighter hydrogen molecules, and the strongly hindered rotational modes (llibrons) for the heavier nitrogen and oxygen molecules. To date, this degree of porosity has not been detected for other ice phases, at least in the low-pressure regime.
In addition, owing to the high performance of TOSCA in the energy transfer region 3‑100 meV, the measurement of the density of states of the empty and the refilled ice XVII made it possible for them to observe the changes to the lattice and librational modes of the water molecules caused by the presence of the gas molecules.
The versatility of ice XVII in terms of its porosity, together with the theoretically infinite number of possible absorption/desorption cycles, make this system an interesting material for energy applications such as hydrogen solid-state storage, or gas sequestration and purification by molecular sieving mechanisms. It could be that an environmentally friendly solution to these challenges is, quite literally, on tap.
Related publication: “Microscopic dynamics of gas molecules confined in porous channel-like ice structure" Journal of Chemical Physics, 160, 154707 (2024). Special Topic: “Porous Solids for Energy Applications".
DOI: 10.1063/5.0201961
Funding: European Union – NextGeneration EU, within PRIN 2022, PNRR M4C2, Project “E-ICES" 2022NRBLPT_PE3_PRIN2022 (CUP: B53D23004390006). DIITET-CNR with the projects “TIRS" (DIT.AD022.180, CUP: B55F20002150001) and “STRIVE" (DIT.AD022.207, CUP: B53C22010110001). Fondazione CR Firenze with the project “Grandi Attrezzature" (Grant No. 2019.0244). European Union – Next Generation EU from the Italian Ministry of Environment and Energy Security POR H2 AdP MMES/ENEA with involvement of CNR and RSE, PNRR – Mission 2, Component 2, Investment 3.5 “Ricerca e sviluppo sull'idrogeno" (PRR.AP015.017 H2 - AdC ENEA/CNR POR IDROGENO, CUP: B93C22000630006).
Authors: L. del Rosso, D. Colognesi, A. Donati (Consiglio Nazionale delle Ricerche - Istituto di Fisica Applicata “Nello Carrara", Italy), S. Rudić (ISIS Neutron and Muon Source, STFC-RAL, U.K.), and M. Celli (Consiglio Nazionale delle Ricerche - Istituto di Fisica Applicata “Nello Carrara", Italy)
Corresponding Author: Leonardo del Rosso (l.delrosso@ifac.cnr.it)
